1. Field of the Invention
This invention relates to an article provided with flame spray coating for increasing wear resistance and/or strength, and a method of producing a flamespray-coated article and flame spraying powder.
2. Description of the Prior Art
Recently, an internal combustion engine such as for a vehicle comes to be formed of a light alloy such as an aluminum alloy in order to lighten the engine. However, since light alloys are generally inferior in mechanical strength such as wear resistance, sliding surfaces are generally provided with flame spray coating of a hard metal, a ceramic or the like in order to improve durability.
For example, it has been proposed to provide a flame spray coating of high-carbon steel and molybdenum on the seal sliding surfaces on which the side seals, the corner seals and the oil seals mounted on the rotor of a Wankel engine slide as disclosed in Japanese Utility Model Publication No. 46(1971)-20083 and the like.
As flame spraying powder which can form flame spray coating at low cost, there has been known powder of Cr.sub.3 C.sub.2. However, if Cr.sub.3 C.sub.2 powder is flamesprayed by itself, good coating cannot be obtained. In order to overcome the problem, there has been proposed flame spray coating powder obtained by adding 15-50 wt % Ni-Cr alloy (including 20% Cr) to Cr.sub.3 C.sub.2 powder.
In the powder, Ni.Cr functions as binder and hard coating of Cr.sub.3 C.sub.2 is formed. The powder is obtained by mixing Cr.sub.3 C.sub.2 powder with ground Ni-Cr alloy. As the particle size of the Ni-Cr alloy powder becomes smaller, the contact area of the Ni-Cr alloy particles with the Cr.sub.3 C.sub.2 particles is increased and the binding power of the Ni-Cr alloy is increased, whereby film properties (hardness, binding power, porosity) become better.
However, due to high ductility and malleability of Ni.Cr and Ni-Cr alloy, Ni-Cr alloy is apt to be ground into flaky pieces and cannot be ground into fine particles. Accordingly, it has been very difficult to obtain fine particles adapted to form flame spray coating having excellent film properties at acceptable cost.